1. Field of the Invention
The present invention relates to a multifocal intraocular lens simulator and a method of simulating a multifocal intraocular lens.
2. Description of the Related Art
A cataract surgery treatment, in which the crystalline lens that has developed an opacification is removed and replaced by an intraocular lens (IOL) to restore the lens's transparency, has become a common surgery treatment. On the other hand, multifocal intraocular lenses are used not only for the treatment of cataracts but also for compensating the age-related decline in accommodation ability. The multifocal intraocular lens has different refractive powers: a primary refractive power, and at least one additional refractive power which corresponds to the primary refractive power to which a differential refractive power is added. Two types of the multifocal intraocular lenses are known in the art: a refractive type, and a diffractive type. The refractive type of multifocal intraocular lens has a lens surface composed of different surface areas having different curvature radiuses, the diffractive type of multifocal intraocular lens has a diffractive structure, and either of these two types of multifocal intraocular lenses forms a plurality of light converging points (one for distance vision and another for near vision) at different positions in an optical axis direction. This lens structure makes it possible for the wearer to secure sufficient eyesight at either a light converging point for distance vision or a light converging point for near vision, thus making it possible for the wearer to carry out everyday activities without having to rely on eyeglasses.
However, at least one of the two light converging points is seen as blurred image, so that this blur becomes noise, thus becoming a cause of deterioration in visibility such as contrast, etc. For instance, the diffractive multifocal intraocular lens has a disadvantage of glare (highlight glare) tending to occur, and the refractive multifocal intraocular lens has a disadvantage of a halo (optical phenomenon) tending to occur around a light (s), especially at night time. These phenomena are due to side effects of the multifocal intraocular lens implant surgery, so that a normal (healthy) eye does not visually identify such phenomena. Accordingly, one visually recognizes such phenomena only after he or she has received multifocal intraocular lens implant surgery (namely, he or she cannot actually experience (perceive) such optical phenomena before receiving such surgery).
Japanese Patent No. 3,814,017 discloses an ocular optical system simulation apparatus. In this apparatus, an intraocular lens is placed in an optical path of an imaging optical system, an image corresponding to a retinal image is captured by an image sensor such as a CCD sensor and the image is then displayed on a display monitor. According to this apparatus, an image corresponding to a retinal image is visually exhibited via an image sensor and a display monitor, and accordingly, biological factors regarding as to what sort of image processing is performed in actual human vision cannot be reflected.
Japanese Patent Domestic Announcement No. 2007-527263 discloses an apparatus devised for the fitting process for multifocal contact lenses. This apparatus synthesizes images obtained through lenses with different diopters with an addition lens being inserted into one of two branch optical paths bifurcated at some midpoint in an optical path. Although one can actually look into this apparatus to see a synthesized image, he or she cannot actually perceive the difference between capabilities of various multifocal intraocular lenses. This is because a different optical technique is used in multi-focalization by image synthesis from that in multi-focalization of an actual intraocular lens; and therefore, the apparatus disclosed in Japanese Patent Domestic Announcement No. 2007-527263 cannot depict the difference in visibility (how one sees objects) between different pupil diameters, which is a matter that can be made evident using, e.g., a refractive type of multifocal intraocular lens.
Meanwhile, multifocal intraocular lenses produced in recent years have a basic lens structure such that the energy distribution of light quantity for distance vision and near vision varies depending on the pupil diameter, regardless as to whether the lenses are of a refractive type or a diffractive type. However, such an energy distribution varies depending on the design philosophy for the lens, so that how a multifocal intraocular lens acts on the eye depends largely on the pupil diameter. Namely, how one sees objects through a multifocal intraocular lens varies depending on the pupil diameter. Since the pupil diameter varies according to light intensity and ones mental state, it is desirable that the multifocal intraocular lens simulator be equipped with the capability of monitoring or controlling the pupil diameter when one sees through the simulator.